BACKGROUND: The main goal of therapy in hepatitis C virus (HCV) infection is to achieve a sustained virological response (SVR). However, the impact of the pharmacological properties of ribavirin on the SVR has not been fully investigated. AIM: To evaluate, through a prospective study, the association between ribavirin plasma level and SVR response in HCV patients treated with pegylated interferon (PEG-IFN) and ribavirin. PATIENTS AND METHODS: Patients treated with PEG-IFN and ribavirin had plasmatic ribavirin dosage at weeks 4 and 12. SVR was evaluated 6 months after the end of treatment. RESULTS: At week 4, a strong correlation was found between HCV-RNA and C(min) of ribavirin plasma level (r = -0.376, P = 0.002) and AUC(0-->12h) of ribavirin plasma level (r = -0.277, P = 0.018). At week 12, a strong correlation was found between HCV-RNA and C(min) of ribavirin plasma level (r = -0.384, P < 0.0001) and AUC(0-->12h) of ribavirin plasma level (r = -0.257, P = 0.002). In genotype 1 patients, AUC(0-->12h) ribavirin and C(min) were significantly correlated with negative HCV-RNA at week 12 and SVR. In the multiple logistic regression model, the only factor independently associated with SVR in genotype 1 patients was negative HCV-RNA at week 12. CONCLUSION: C(min) of ribavirin at weeks 4 and 12 was significantly higher in sustained virological responders compared with relapser or nonresponder patients. However, in genotype 1 patients, plasma ribavirin level at weeks 4 and 2 was not associated with SVR.